Screening and identification of the dominant antigens of the African swine fever virus

Development of a P30 protein-based indirect ELISA for detecting African swine fever antibodies utilizing the HEK293F expression system

African swine fever (ASF) is an acute, febrile, and highly lethal infectious disease in pigs caused by the African swine fever virus (ASFV). Effective detection methods and strict biosecurity measures are crucial for preventing and controlling ASF, especially since there are currently no commercially available vaccines or antiviral drugs to combat ASFV infection effectively. However, the emergence of low-virulence strains of ASFV in recent years has led to false-positive results, highlighting the importance of early-produced antibody detection methods. Therefore, detecting antibodies against ASFV produced early in the infection can facilitate the prompt identification of infected pigs. This study focused on the p30 protein, an early expressed protein during ASFV infection, to develop an indirect ELISA. This method was established using the HEK293F suspension cell expression system, which has the ability to produce large quantities of correctly folded proteins with normal functionality. In this study, we developed an indirect ELISA test utilizing the p30 recombinant protein produced by the HEK293F suspension cell expression system as the antigen coating. The concentration of the p30 protein obtained from the HEK293F suspension cell expression system was measured at 4.668 mg/mL, serving as the foundation for establishing the indirect ELISA. Our findings indicate that the indirect ELISA method exhibits a sensitivity of 1:12800. Furthermore, it demonstrates high specificity and excellent reproducibility. Comparing our results to those obtained from the commercial kit, we found a coincidence rate of 98.148 % for the indirect ELISA. In summary, we have developed a sensitive method for detecting ASFV, providing a valuable tool for monitoring ASFV infection in pig herds.

African swine fever virus pB475L evades host antiviral innate immunity via targeting STAT2 to inhibit IFN-I signaling

African swine fever virus (ASFV) causes severe disease in domestic pigs and wild boars, seriously threatening the development of the global pig industry. Type I interferon (IFN-I) is an important component of innate immunity, inducing the transcription and expression of antiviral cytokines by activating Janus-activated kinase-signal transducer and activator of transcription (STAT). However, the underlying molecular mechanisms by which ASFV antagonizes IFN-I signaling have not been fully elucidated. Therefore, using coimmunoprecipitation, confocal microscopy, and dual luciferase reporter assay methods, we investigated these mechanisms and identified a novel ASFV immunosuppressive protein, pB475L, which interacts with the C-terminal domain of STAT2. Consequently, pB475L inhibited IFN-I signaling by inhibiting STAT1 and STAT2 heterodimerization and nuclear translocation. Furthermore, we constructed an ASFV-B475L7PM mutant strain by homologous recombination, finding that ASFV-B475L7PM attenuated the inhibitory effects on IFN-I signaling compared to ASFV-WT. In summary, this study reveals a new mechanism by which ASFV impairs host innate immunity.

Immunogenicity Analysis and Identification of Potential T-Cell Epitopes in C129R Protein of African Swine Fever Virus

The highly conserved C129R protein of AFSV was utilized in the development of an ASFV recombinant adenovirus vaccine, demonstrating strong immunogenicity. In this study, we immunized 6-week-old female C57BL/6J mice via subcutaneous injection with 10 μg of purified C129R protein. Humoral and cellular immune effects were assessed using ELISA, flow cytometry, and ELISpot assays. Additionally, 19 peptides of the C129R protein were synthesized and screened for the use of bioinformatics. Positive T-cell epitopes were screened using ELISpot. The results indicated a higher proportion of CD4+ and CD8+ T lymphocytes in immunized mice compared to control mice. ELISA analysis revealed a serum titer of approximately 1:1, 638, 400 in the experimental group of mice. Additionally, peptides C11(53-61aa), C14(81-89aa), C16(97-105aa), and C18(116-124aa) from the C129R protein were able to activate mice spleen lymphocytes to produce IFN-γ. These findings suggest that the C129R protein significantly enhances both humoral and cellular immunity in immunized mice. Moreover, peptides C11, C14, C16, and C18 may serve as potential T-cell epitopes for the C129R protein. These results lay the groundwork for the further exploration of ASFV C129R protein and the identification of novel ASF vaccine antigens.

A vesicular stomatitis virus-based African swine fever vaccine prototype effectively induced robust immune responses in mice following a single-dose immunization

Introduction

African swine fever (ASF) is a highly contagious hemorrhagic fever disease in pigs caused by African swine fever virus (ASFV). It is very difficult to control and prevent ASF outbreaks due to the absence of safe and effective vaccines.

Methods

In order to develop a safe and effective ASF vaccine for the control and prevention of ASF, two ASFV recombinant vesicular stomatitis virus (VSV) live vector vaccine prototypes, containing the gene of p72, and a chimera of p30 and p54, were developed based on the replication-competent VSV, and named VSV-p72 and VSV-p35. The immune potency of VSV-p72 or VSV-p35 alone and in combination was evaluated in BALB/c mice via intramuscular and intranasal vaccination.

Results

The results indicated that whether administered alone or in combination, the two vaccine prototypes showed acceptable safety in mice and, more importantly, induced high-level specific antibodies against p72, p30, and p54 of ASFV and a strong cellular immune response 28 days after vaccination. The sera from mice vaccinated with the vaccine prototypes significantly inhibited ASFV from infecting porcine alveolar macrophages (PAMs) in vitro. Most notably, the immunized sera from a mixture of VSV-p35 and VSV-p72 inhibited ASFV from infecting PAMs, with an inhibition rate of up to 78.58%.

Conclusion

Overall, our findings suggest that ASFV recombinant VSV live vector vaccine prototypes may become a promising candidate vaccine for the control and prevention of ASF.

Identification of Linear Epitopes in the C-Terminal Region of ASFV p72 Protein

African swine fever, which is induced by the African swine fever virus (ASFV), poses a significant threat to the global pig industry due to its high lethality in domestic pigs and wild boars. Despite the severity of the disease, there is a lack of effective vaccines and drugs against the ASFV. The p72 protein, constituting 31 to 33% of the total virus particle mass, serves as the primary capsid protein of ASFV. It is a crucial antigen for the development of ASF subunit vaccines and serological diagnostic methods. In this investigation, 27 monoclonal antibodies (mAbs) were generated through mouse immunization with the truncated C-terminal p72 protein expressed by Escherichia coli. Among these, six mAbs exhibited binding to the p72 trimer, with their respective recognized epitopes identified as 542VTAHGINLIDKF553, 568GNAIKTP574, and 584FALKPREEY592. All three epitopes were situated within the interval sequences of functional units of the C-terminal jelly-roll barrel of p72. Notably, two epitopes, 568GNAIKTP574 and 584FALKPREEY592, were internal to the p72 trimer, while the epitope 542VTAHGINLIDKF553 was exposed on the surface of the trimer and consistently conserved across all ASFV genotypes. These findings enhance our comprehension of the antigenic function and structure of the p72 protein, facilitating the utilization of p72 in the development of diagnostic techniques for ASFV.